1. Field of the Invention
The present invention generally relates to compressor valves in a piston compressor. In particular, the invention relates to a method and apparatus for controlling the movement of a sealing element of a suction valve within a piston compressor by means of a control device.
2. Description of the Conventional Art
The useful life of an automatic compressor valve used mostly on the suction and pressure side is influenced primarily by the impact loading during the alternating impacting of an actual sealing element on a valve seat and/or valve stop. In particular, the sealing element is in a closed position when the pressure inside a cylinder chamber is greater than or equal to the counter-pressure of a suction chamber. When the counter-pressure of the suction chamber exceeds the falling pressure of the cylinder chamber (i.e., underpressure in the cylinder chamber), the sealing element is forced into an open position. Due to the rapid underpressure produced in the cylinder chamber, the sealing element, when moving toward an open position, accelerates at high speed in the direction of the valve stop. This rapid acceleration creates an undesirable loading impact on the sealing element which in turn adversely diminishes the useful life of the compressor valve.
In the case of a suction valve, by corresponding choice of the spring system, the closing speed can be kept sufficiently low to reduce the closing impact. For instance, to reduce the opening impact, a system of so-called double damping is used, which, after overcoming part of a stroke, the sealing element impacts on a damping plate or the like, movable in the direction of opening, is thereby braked and then, together with the damping plate, overcomes the remaining stroke, whereby the clearly enlarged moving mass causes a further decrease in the acceleration of the sealing element, resulting in a clearly reduced impact speed of the sealing element at the valve stop, compared with the simple valve of this kind.
Furthermore, compressor arrangements have become known in which, with the aid of so-called lift lugs (unloaders), on the one hand a capacity adjustment, continuously variable within certain limits, is brought about by partial holding open of the suction valve during the compression stroke, and in which, on the other hand, by corresponding dimensioning of the mass of the lift lug as well as the arrangement of motion damper, a lowering of the impact speed of the sealing element during closing is achieved.
To some extent the aforementioned arrangements also can be used to reduce the impact speed of the sealing element during opening: the lift lug is pressed by means of a spring against the sealing element or valve plate and, in any case, is already sitting there for a while before the pressure balance is attained. The additional opening force caused by this pressure spring may also open the sealing element under certain circumstances already before the pressure balance is attained. In this regard, however, the mass of the lift lug must be accelerated by the spring force against the overpressure in the cylinder chamber. Since the mass of such lift lugs is necessarily relatively great compared with the mass of the sealing elements used, in any case only a slight acceleration results and the premature opening of the sealing element caused by this under certain circumstances is minor.